Real Time LiDAR Signal Processing FPGA Modules

ABSTRACT

Aspects of the present disclosure involve a system and method for performing time of flight estimation of a laser pulse using a LiDAR signal processing. A plurality of digital waveforms are correlated to a transmitted pulse for time of flight estimation. Each of the plurality of digital waveforms can be correlated independently by a corresponding correlator in a plurality of correlators working in parallel. Each of the correlators can include signal processing modules for time of flight estimation including an interpolating filters and peak detect modules.

TECHNICAL FIELD

This disclosure relates generally to LiDAR signal processing, and morespecifically to a method for performing time of flight estimation of alaser pulse using LiDAR signal processing.

BACKGROUND

Light Detection and Ranging (LiDAR) is a remote sensing technology thatuses light pulses to measure ranges or distances of an object. It is atechnology that has application in various fields including archeology,meteorology, bathymetry, etc. Further, the information extracted fromthese measurements can have many uses, including determining surfacecharacteristics, creating elevation models, and even obtainingthree-dimensional (3-D) images of an object at a distance. To determinethe 3-D image of an object at a distance, time differences (or time offlight estimations) are determined between the transmission of laserlight pulses and the reception of the reflected signals. Generally,conventional components used in providing these time of flightestimations can be slow, inaccurate, or too large to provide thecapabilities required in applications like space exploration andmilitary surveillance.

BRIEF SUMMARY

The present disclosure is directed to an apparatus and methods forperforming time of flight estimation. The apparatus can include a mirrorelectrically coupled to a laser used for transmitting a first laserpulse generated by the laser in a first direction to yield a firstreflected laser pulse and a second laser pulse generated by the laser ina second direction to yield a second reflected laser pulse. Theapparatus can further include a receiver electrically coupled to themirror positioned in the first direction of the mirror and receiving thefirst reflected laser pulse and positioned in the second direction ofthe mirror and receiving the second reflected laser pulse. The apparatuscan also include an analog-to-digital converter electrically coupled tothe receiver for digitizing the first reflected laser pulse to produce afirst digital waveform and digitizing the second reflected laser pulseto produce a second digital waveform. The apparatus can also include afirst correlator electrically coupled to the analog-to-digital converterfor determining a first time of flight estimate of the first digitalwaveform and a second correlator electrically coupled to theanalog-to-digital converter for determining a second time of flightestimate of the second digital waveform. The apparatus can include aprocessor electrically coupled to the first correlator and the secondcorrelator, the processor processing the first time of flight estimateand the second time of flight estimate to determine a range of anobject.

In another aspect, an apparatus can include a receiver receiving aplurality of radio frequency pulses, wherein each radio frequency pulsein the plurality of radio frequency pulses corresponds to a pixel. Theapparatus can also include an analog-to-digital converter electricallycoupled to the receiver, the analog-to-digital converter digitizing eachradio frequency pulse into a corresponding digital waveform. Theapparatus can include a plurality of correlators electrically coupled tothe analog-to-digital converter, wherein each of the plurality ofcorrelators determines a time of flight for the corresponding digitalwaveform. The apparatus can further include a processor electricallycoupled to the plurality of correlators, the processor determining animage of an object, based in part on the time of flight determined byeach of the plurality of correlators.

The method can include receiving, by a receiver, a plurality of radiofrequency pulses, wherein each radio frequency pulse in the plurality ofradio frequency pulses corresponds to a pixel. The method can furtherinclude digitizing, by an analog-to-digital converter, each radiofrequency pulse into a corresponding digital waveform. The method canalso include determining, by a plurality of correlators, a time offlight for the corresponding digital waveform and determining, by aprocessor, an image of an object, based in part on the time of flightdetermined by each of the plurality of correlators.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will be more fully understood with reference to thefollowing figures and charts, which are presented as various embodimentsof the disclosure and should not be construed as a complete recitationof the scope of the disclosure, wherein:

FIG. 1 is a diagram illustrating an example system architecture.

FIG. 2 is a block diagram illustrating a system for performing time offlight estimation of a laser pulse using LiDAR signal processing.

FIG. 3 is a flow chart of a method for performing time of flightestimation of a laser pulse using LiDAR signal processing.

DETAILED DESCRIPTION

Aspects of the present disclosure involve systems, methods, devices andthe like for performing time of flight estimation of a laser pulse usinga LiDAR signal processing. In one aspect, a plurality of digitalwaveforms are correlated to a transmitted pulse for time of flightestimation. Each of the plurality of digital waveforms can be correlatedindependently by a corresponding correlator in a plurality ofcorrelators. The plurality of correlators can work in parallel in orderto determine time of flight estimates in real time. The system may befine-tuned such that a desired speed may be accomplished byinstantiating a corresponding number of correlators on afield-programmable gate array (FPGA).

In another aspect, each of the correlators can include signal processingmodules for time of flight estimation. For example, noise may beextracted from the digital waveforms using a threshold module, which maybe designed to ensure that the information received is real data byplacing a threshold value on the signal which provides a minimum levelof correlation that should be achieved to be considered valid. That isto say, the data received is analyzed to confirm a given correlationlevel is surpassed, otherwise the information is considered noise. Asanother example, the correlator can include a peak detect module whichmay be design to detect the peak in the digital waveform for comparisonwith the peak in the transmitted pulse.

FIG. 1 is a diagram of an architecture 100 for performing time of flightestimation. Conventionally, radio interferometry architectures includeradio frequency components which can be high powered components. Thecomponents can generate noise and heat which can lead to unreliableand/or unstable measurements. To overcome the heat and instability,multiple correlator components are introduced on an FPGA which canprovide better signal stability for time of flight estimations.

FIG. 1 introduces the general architectural components for a system thatcan be used in performing time of flight estimation of a laser pulseusing LiDAR signal processing. FIG. 1 discloses some basic hardwarecomponents that can apply to system examples of the present disclosure.An exemplary system and/or computing device 100 is introduced thatincludes a processing unit (CPU or processor) 110 and a system bus 105that couples various system components, including the system memory 115,read only memory (ROM) 120, and random access memory (RAM) 125 to theprocessor 110. The system 100 can include a cache 112 of high-speedmemory connected directly with, in close proximity to, or integrated aspart of the processor 110. The system 100 copies data from the memory115/120/125 and/or the storage device 130 to the cache 112 for quickaccess by the processor 110. In this way, the cache provides aperformance boost that avoids processor 110 delays while waiting fordata These and other modules can control or be configured to control theprocessor 110 in the performance of various operations or actions. Othersystem memory 115 may be available for use as well. The memory 115 caninclude multiple different types of memory with different performancecharacteristics. It can be appreciated that the disclosure may operateon a computing device 100 with more than one processor 110 or on a groupor cluster of computing devices networked together to provide greaterprocessing capability. The processor 110 can include any general purposeprocessor and a hardware module or software module, such as module 1132, module 2 134, and module 3 136, stored in storage device 130, orstandalone light detection and ranging (LiDAR) processing module 114configured to control the processor 110 as well as a special-purposeprocessor where software instructions are incorporated into theprocessor. The processor 110 may be a self-contained computing system,containing multiple cores or processors, a bus, a memory controller, acache, etc. A multi-core processor may be symmetric or asymmetric. Theprocessor 110 can include multiple processors, such as a system havingmultiple, physically separate processors in different sockets, or asystem having multiple processor cores on a single physical chip.Similarly, the processor 110 can include multiple distributed processorslocated in multiple separate computing devices, but working togethersuch as via a communications network. Multiple processors or processorcores can share resources such as memory 115 or cache 112, or canoperate using independent resources. The processor 110 can include oneor more of a state machine, an application specific integrated circuit(ASIC), or a programmable gate array (PGA) including a field PGA.

The system bus 105 may be any of several types of bus structures,including a memory bus or memory controller, a peripheral bus, and alocal bus using any of a variety of bus architectures. A basicinput/output (BIOS) stored in ROM 120 or the like may provide a basicroutine that helps to transfer information between elements within thecomputing device 100, such as during start-up. The computing device 100further includes storage devices 130 or computer-readable storage mediasuch as a hard disk drive, a magnetic disk drive, an optical disk drive,a tape drive, a solid-state drive, a RAM drive, a removable storagedevice, a redundant array of inexpensive disks (RAID), a hybrid storagedevice, or the like. The storage device 130 is connected to the systembus 105 by a drive interface. The drives and the associatedcomputer-readable storage devices provide nonvolatile storage ofcomputer-readable instructions, data structures, program modules, andother data for the computing device 100. In one aspect, a hardwaremodule that performs a particular function includes the softwarecomponent stored in a tangible computer-readable storage device inconnection with the necessary hardware components, such as the processor110, bus 105, display (or any output device) 135, and so forth, to carryout a particular function. In another aspect, the system can use aprocessor and a computer-readable storage device to store instructionswhich, when executed by the processor, cause the processor to performoperations, a method or other specific actions. The basic components andappropriate variations can be modified depending on the type of device,such as whether the device 100 is a small, handheld computing device, adesktop computer, or a computer server. When the processor 110 executesinstructions to perform “operations,” the processor 110 can perform theoperations directly and/or facilitate, direct, or cooperate with anotherdevice or component to perform the operations.

Although the exemplary embodiment(s) described herein employs the harddisk 130, other types of computer-readable storage devices which canstore data that are accessible by a computer, such as magneticcassettes, flash memory cards, digital versatile disks (DVDs),cartridges, random access memories (RAMs) 125, read only memory (ROM)120, a cable containing a bit stream and the like, may also be used inthe exemplary operating environment. According to this disclosure,tangible computer-readable storage media, computer-readable storagedevices, computer-readable storage media, and computer-readable memorydevices expressly exclude media such as transitory waves, energy,carrier signals, electromagnetic waves, and signals per se.

To enable user interaction with the computing device 100, an inputdevice 145 can be any number of input mechanisms, such as a microphonefor speech, a touch-sensitive screen for gesture or graphical input, akeyboard, a mouse, a motion input, speech and so forth. An output device135 can also be one or more of a number of output mechanisms known tothose of skill in the art. In some instances, multimodal systems enablea user to provide multiple types of input to communicate with thecomputing device 100. The communications interface 140 generally governsand manages the user input and system output. There is no restriction onoperating on any particular hardware arrangement, and therefore thebasic hardware depicted may easily be substituted for improved hardwareor firmware arrangements as they are developed.

For clarity of explanation, the illustrative system embodiment ispresented as including individual functional blocks, includingfunctional blocks labeled as a “processor” or processor 110. Thefunctions of these blocks may be provided through the use of eithershared or dedicated hardware, including, but not limited to, hardwarecapable of executing software and hardware, such as a processor 110,that is purpose-built to operate as an equivalent to software executingon a general purpose processor. For example, the functions of one ormore processors presented in FIG. 1 can be provided by a single sharedprocessor or multiple processors (use of the term “processor” should notbe construed to refer exclusively to hardware capable of executingsoftware). Illustrative embodiments may include microprocessor and/ordigital signal processor (DSP) hardware, read-only memory (ROM) 120 forstoring software performing the operations described below, and randomaccess memory (RAM) 125 for storing results. Very large scaleintegration (VLSI) hardware embodiments, as well as custom VLSIcircuitry in combination with a general purpose DSP circuit, may also beprovided.

The logical operations of the various embodiments are implemented as:(1) a sequence of computer implemented steps, operations, or proceduresrunning on a programmable circuit within a general use computer; (2) asequence of computer implemented steps, operations, or proceduresrunning on a specific-use programmable circuit; and/or (3)interconnected machine modules or program engines within theprogrammable circuits. The system 100 shown in FIG. 1 can practice allor part of the recited methods, can be a part of the recited systems,and/or can operate according to instructions in the recited tangiblecomputer-readable storage devices. Such logical operations can beimplemented as modules configured to control the processor 110 toperform particular functions according to the programming of the module.For example, FIG. 1 illustrates four modules: Mod1 132, Mod2 134, Mod3136, and LiDAR processing module 114, which are configured to controlthe processor 110. These modules may be stored on the storage device 130and loaded into RAM 125 or memory 115 at runtime or may be stored inother computer-readable memory locations. Alternatively, these modulesmay be standalone such as an independent breadboard with FPGAs mountedon it, (e.g., LiDAR processing module 114) for controlling the LiDARsignal processing.

LiDAR processing module 114 can use the computing device 100 of FIG. 1or similar computer components to perform LiDAR signal processing andcorrelation. LiDAR processing module 114 can be one or more componentsas disclosed below and in conjunction with FIG. 2 for time of flight andobject image estimation. For example, LiDAR processing module 114 caninclude a laser source, a microelectromechanical system (MEMS) mirror, adigitizer, correlators, waveform averaging components,serializer/deserializers, and the like for performing LiDAR signalprocessing. Additionally or alternatively, LiDAR processing module 114can independently process or work jointly with processor 110 fordetermining the time of light of the laser pulses emitted by the laserin order to obtain range and image of an object.

One or more parts of the example computing device 100, up to andincluding the entire computing device 100, can be virtualized. Forexample, a virtual processor can be a software object that executesaccording to a particular instruction set, even when a physicalprocessor of the same type as the virtual processor is unavailable. Avirtualization layer or a virtual “host” can enable virtualizedcomponents of one or more different computing devices or device types bytranslating virtualized operations to actual operations. Ultimatelyhowever, virtualized hardware of every type is implemented or executedby some underlying physical hardware. Thus, a virtualization computelayer can operate on top of a physical compute layer. The virtualizationcompute layer can include one or more of a virtual machine, an overlaynetwork, a hypervisor, virtual switching, and any other virtualizationapplication.

The processor 110 can include all types of processors disclosed herein,including a virtual processor. However, when referring to a virtualprocessor, the processor 110 includes the software components associatedwith executing the virtual processor in a virtualization layer and theunderlying hardware necessary to execute the virtualization layer. Thesystem 100 can include a physical or virtual processor 110 that receivesinstructions stored in a computer-readable storage device, which cancause the processor 110 to perform certain operations. When referring toa virtual processor 110, the system also includes the underlyingphysical hardware executing the virtual processor 110.

In some embodiments, the core processing unit in the system can be theGoddard Space Flight Center (GSFC)-developed SpaceCube, a hybridcomputing platform designed to provide command and data handlingfunctions for earth-orbiting satellites. The SpaceCube includes fiveslices (cards): two Power Slices, two Processor Slices, and one VideoControl Module (VCM) Slice. Other configurations are possible. Eachprocessor slice contains two Xilinx Virtex Field Programmable GateArrays (FPGAs), and each FPGA contains two PPC405 processors running at250 MHz. These eight processors host multiple instantiations of thesystem pose application FPose, along with command and telemetry handlingsoftware that allows a flight-like ground terminal to control the systemremotely. The VCM provides sensor data compression and 16 Gb of flashmemory to store raw sensor images for later playback. The ArgonSpaceCube is an engineering development unit (EDU) version of thehardware own on the (Relative Navigation Sensor) RNS experiment andMaterials International Space Station Experiment.

As indicated, FIG. 1 introduces the general architectural components andspecifically the use of LiDAR processing module 114 for performingflight time estimation using LiDAR signal processing. FIG. 2 discloses ablock diagram of a system 200 for performing such estimation. In someinstances, optical signal module 114 can perform some or all of theLiDAR signal processing functions/operations described herein. Forexample, in one embodiment, system 200 can be a standalone component(e.g., breadboard) that includes a laser source 206 that generates lightpulses that then get reflected, digitized by an analog-to-digitalconverter (ADC) 202 and measured using correlators 210 located in anintegrated circuit (IC) 216 to determine time of flight estimations thatcan be used to obtain a range of an object. In particular, system 200can be used to process images in real time by creating many parallelblocks of digital correlators within the IC 216 which provide the highthroughput that enables the real time estimations and image scans withsix degrees of freedom. Alternatively, system 200 can include separatemodules which can include the ADC 202, microelectromechanical systems(MEMS) 204, and laser source 206, while IC 216 resides on an independentbreadboard.

As conventionally understood, LiDAR includes the emission of laserpulses of light used to determine the range to a distant object. Thedistance to the object is determined by measuring the time delay betweenthe emission of the laser pulse of light and the detection of thereflected signal using a correlator. System 200 illustrates the use oflaser source 206 which may create the laser pulse. In oneimplementation, a LiDAR system a mirror may be used to guide the laserpulse in a specific direction. In a particular implementation, a MEMSmirror 208, which may be located in microclectromechanical system (MEMS)204, may be used for guiding the laser pulse. The MEMS system 204 mayinclude the MEMS mirror 208 and any other control that may be requiredto position the mirror such that the laser pulse generated by the lasersource 206 is transmitted in a desired direction towards the object at adistance. In one embodiment, the laser pulse can be used to representone pixel on the object. A slight movement of the MEMS mirror 208 canthen be used to position the transmission of the laser pulse in a seconddirection to capture a second pixel. Therefore, to obtain detailedmeasurements of the object, multiple laser pulses may be transmittedsuch that the MEMS mirror 208 is moved slightly as a next pulse istransmitted, the next pixel is measured. In the current embodiment, themirror may continue to move ever so slightly in a round robin mannersuch that every slight move from the mirror represents a new pixel.

As the pulse is transmitted toward an object, the signal is reflectedand captured by a receiver (not shown) and transmitted to theanalog-to-digital converter 202. The incoming signal/waveform iscaptured and digitized by the analog-to-digital converter 202 inpreparation for processing. In one embodiment, the analog-to-digitalconverter 202 can be a high speed converter which can sample twochannels with about 512 samples each. For example, the high speeddigital converter can sample a pixel every 5 microsecs, capturing boththe waveform's in-phase and quadrature components.

The sampled data can then be stored in a first-in first-out (FIFO)buffer 234 before being processed by correlator(s) 210. The FIFO buffer234 may be filled with the captured data from the analog-to-digitalconverter 202 and stored such that it can be clocked out sample bysample to an interpolating finite impulse response (FIR) filter 226located in correlator 210. An FIR filter may be a filter that is used tofind coefficients and filter order that meets certain criteria. Forexample. Interpolating FIR 216 can be designed to interpolate thesamples by a factor of 16 in order to improve range or time resolutionin time of flight estimate. Further, the interpolating FIR 216 can beimplemented as a matched filter.

Next, to ensure the samples processed are real data and not noise, thedata gets processed through an apply thresholds module 228. Applythreshold module 228, is a module that may be designed to ensure thatthe information received is real data, by placing a threshold value onthe signal which provides a minimum level of correlation that should beachieved to be considered valid. That is to say, the data received isanalyzed to confirm a given correlation level is surpassed otherwise theinformation is considered noise. In one example, different levels ofvalidity may be applied for the in-phase and quadrature samples, asdifferent noise levels may exist.

Once the samples filtered are confirmed to be real data, the data isprocessed to select the highest peak in 230. That is to say, the highestpeak from the filtered samples is detected and used to compare againstan ideal Gaussian (in RX_pk-TX_pk 232). In some instances, thetransmitted laser pulse may be an ideal Gaussian pulse therefore, a peakfrom an ideal pulse (TX_pk) may be compared against the received sampledpeak (RX_pk) which can then be analyzed to determine an object range andimage. In some instances, highest peak as well as the lowest and midpeak may be identified. This may be especially useful in applicationswhere foliage penetration is necessary. Further, in one implementation,the ideal transmitted pulse and received samples can be compared andconcatenated into the same waveform and fed into correlator 210 for animproved time of flight estimation. If a good signal to ratio isachieved, then jitter that may be generated by triggering the laserpulse may be subtracted and estimation improved.

Note that this process may be repeated for each incoming reflectedsignal corresponding to a transmitted pulse. As indicated, each pulserepresents a pixel in an object and thus many pulses may be transmitted,reflected, and correlated. In one specific embodiment, numerouscorrelators may operate in parallel providing the ability to extracttime of flight estimates in real time. In this embodiment, the systemmay be fine-tuned such that the speed desired may be accomplished byinstantiating multiple copies of correlator 210 on a field-programmablegate array (FPGA). For example, in one design, four correlators may runin parallel to achieve 20 pixels per microsecond. In another example,eighteen correlators may be used to process 200,000 pixels permicrosecond. Still yet in another example, eighty correlators may beused to process 4 million pixels per microsecond.

In some instances, prior to entering the correlator 210, the digitizedsamples may be processed by a waveform averaging module 224. Thewaveform averaging module 224 may be designed to average a predeterminednumber of waveforms in order to reduce the received noise. By reducingnoise in the received waveforms (digitized samples), the signal-to-noiseratio (SNR) can be increased and jitter reduced so that cleaner data canbe processed by the correlators 210, producing an image with increasedresolution.

Additionally, other modules and/or controls may be located within IC 216to aid in the processing of the LiDAR signal for image range detectionand time of flight estimation. For example, MEMS controller 212 andlaser controller 214 may be present in IC 216 to help control functionssuch as the direction of the MEMS mirror 208 within MEMS system 204 andfrequency of the laser pulse deriving from the laser source 206.Further, MEMS controller 212 and laser controller 214 can provide aninterface between external modules (e.g., 204, 206) and the IC 216. Asanother example, SerDes 222 may also be present in IC 216 which can helpin the serializing and/or deserializing of the waveform arriving fromthe receiver and digitized by the analog-to-digital converter 202.Further components can be included in IC 216 including processors 218and PLBs 220, in addition to others not illustrated in FIG. 2 which arecommonly known in the art.

FIG. 3 is a flowchart of the various operations of the presentlydisclosed technology. Specifically, FIG. 3 is a flow chart of a methodfor performing time of flight estimation of a laser pulse using LiDARsignal processing. Method 300 begins with operation 302, a reflectedradio frequency (RF) pulse is received at a receiver. The reflected RFpulse may derive from the reflection of an object being scanned at adistance. In some instances, a laser pulse can be transmitted and guidedby a MEMS mirror in the direction of the object for LiDAR signalprocessing and scanning. In these instances, the received reflected RFpulse can represent one pixel on the object at a distance. However, inother instances the reflected RF pulse can represent more than one pixeland/or multiple reflected RF pulses can be received.

Once the reflected pulse has been received, method 300 continues tooperation 304, Where the RF signal gets digitized for processing. Thedigitizing can occur using an analog-to-digital converter. Theanalog-to-digital converter may be a standalone with an interfacecoupling an IC where the signal processing including signal correlationcan occur. Further, the analog-to-digital converter may be coupled to aSerDes for serializing/deserializing the digital waveform. In addition,the analog-to-digital converter may digitize the waveform into in-phaseand quadrature components.

In operation 306, the digital waveform is sent to a correlator forprocessing. The correlator receiving the waveform may be one of multiplecorrelators running in parallel on an FPGA. Further, each correlator canprocess a pixel. In the correlator, multiple modules may be present toprocess the digitized waveform in order to obtain time of flightestimations and achieve 3-D image scanning of the object at a distance.The multiple modules can include an interpolating FIR may function as amatched filter designed to interpolate the samples by a predeterminedfactor in order to improve range or time resolution in time of flightestimate. In addition, an apply thresholds module can also exist, whichis a module that may be designed to ensure that the information receivedis real data, by placing a threshold value on the signal which providesa minimum level of correlation that should be achieved to be consideredvalid. That is to say, the data received is analyzed to confirm a givencorrelation level is surpassed otherwise the information is considerednoise. Once the data is clear of noise, the peak is detected andcompared against the transmitted pulse (e.g., ideal Gaussian pulse)which can then be analyzed to determine an object image and pulse timeof flight in operation 308. In some instances, more than one peak may bedetected and compared for closer correlation approximation. In someinstances, an averaging waveform module may also be used prior to thecorrelator which may be used to average a predetermined number ofwaveforms in order to reduce the received noise. By reducing noise inthe received waveforms (digitized samples), the signal-to-noise ratio(SNR) can be increased and jitter reduced so that cleaner data can beprocessed by the correlators 210, producing an image with increasedresolution.

Once the received RF pulse has been processed, the LiDAR system candetermine in another reflected RF pulse has been detected at operation310. If indeed a new pulse has been detected, then the process returnsto operation 302, where the reflected RF pulse is received and thenprocessed by the analog-to-digital converter and correlator for time offlight estimations in operations 304-308. In one embodiment, the next RFpulse received is processed by the next correlator working in parallelwith the prior correlator. In some instances, four, eighteen, or eveneighty correlators can be used in parallel for processing the image andobtaining real time object range estimates by obtaining time of flightestimates. The correlators can work in a round robin manner such thateach correlator is processing the next incoming pixel of the object at adistance in the form of a reflected RF pulse. Alternatively, if no moreRF pulses are detected, the process can continue to operation 312, wherethe measurement data from the correlators is interrogated andpost-processed to determine the scanned image and range.

Note that the LiDAR processing scheme presented in FIGS. 2-3 is apossible example for performing time of flight estimations using LiDARsignal processing that may be employed or be configured in accordancewith aspects of the present disclosure. It will be appreciated thatother configurations may be utilized.

In the present disclosure, the methods disclosed may be implemented assets of instructions in hardware or software. It may be furtherunderstood that the specific order or hierarchy of steps in the methodsdisclosed are instances of example approaches. Based upon designpreferences, it is understood that the specific order or hierarchy ofsteps in the method can be rearranged while remaining within thedisclosed subject matter. The accompanying method claims presentelements of the various steps in a sample order, and are not necessarilymeant to be limited to the specific order or hierarchy presented.

While the present disclosure has been described with reference tovarious implementations, it will be understood that theseimplementations are illustrative and that the scope of the presentdisclosure is not limited to them. Many variations, modifications,additions, and improvements are possible. More generally, embodiments inaccordance with the present disclosure have been described in thecontext of particular implementations. Functionality may be separated orcombined in blocks differently in various embodiments of the disclosureor described with different terminology. These and other variations,modifications, additions, and improvements may fall within the scope ofthe disclosure as defined in the claims that follow.

What is claimed is:
 1. An apparatus comprising: a mirror electricallycoupled to a laser, the mirror transmitting a first laser pulsegenerated by the laser in a first direction to yield a first reflectedlaser pulse and a second laser pulse generated by the laser in a seconddirection to yield a second reflected laser pulse; a receiverelectrically coupled to the mirror, the receiver positioned in the firstdirection of the mirror and receiving the first reflected laser pulse;an analog-to-digital converter electrically coupled to the receiver, theanalog-to-digital converter digitizing the first reflected laser pulseto produce a first digital waveform; a first correlator electricallycoupled to the analog-to-digital converter, the first correlatordetermining a first time of flight estimate of the first digitalwaveform; the receiver positioned in the second direction of the mirrorand receiving the second reflected laser pulse; the analog-to-digitalconverter digitizing the second reflected laser pulse to produce asecond digital waveform; a second correlator electrically coupled to theanalog-to-digital converter, the second correlator determining a secondtime of flight estimate of the second digital waveform; and a processorelectrically coupled to the first correlator and the second correlator,the processor processing the first time of flight estimate and thesecond time of flight estimate to determine a range of an object.
 2. Theapparatus of claim 1, further comprising: a first interpolating finiteimpulse response (FIR) filter in the first correlator, the firstinterpolating FIR filter filtering the first digital waveform to improvea time resolution of the first time of flight estimate.
 3. The apparatusof claim 2, further comprising: an apply thresholds module electricallycoupled to the first interpolating FIR filter, the apply thresholdsmodule applying a threshold value to the filtered first digital waveformto ensure information data is being processed.
 4. The apparatus of claim3, further comprising: a peak detect module electrically coupled to theapply thresholds module, the peak detect module detecting a first peakin the filtered first digital waveform to compare against a first peakin the transmitted first laser pulse generated by the laser in the firstdirection to produce the first flight time estimate.
 5. The apparatus ofclaim 1, further comprising: a waveform averaging module electricallycoupled to the analog-to-digital converter and the first correlator, thewaveform averaging module averaging the first digital waveform with athird digital waveform to reduce received noise for improvedsignal-to-noise ratio of the first digital waveform at the firstcorrelator.
 6. An apparatus comprising: a receiver receiving a pluralityof radio frequency pulses, wherein each radio frequency pulse in theplurality of radio frequency pulses corresponds to a pixel; ananalog-to-digital converter electrically coupled to the receiver, theanalog-to-digital converter digitizing each radio frequency pulse into acorresponding digital waveform; a plurality of correlators electricallycoupled to the analog-to-digital converter, wherein each of theplurality of correlators determines a time of flight for thecorresponding digital waveform; and a processor electrically coupled tothe plurality of correlators, the processor determining an image of anobject, based in part on the time of flight determined by each of theplurality of correlators.
 7. The apparatus of claim 6, wherein theplurality of correlators are one of four, eighteen, and eightycorrelators working in parallel.
 8. The apparatus of claim 6, furthercomprising: a waveform averaging module electrically coupled to theanalog-to-digital converter and the plurality of correlators, thewaveform averaging module averaging a predetermined number of thecorresponding digital waveforms into an averaged digital waveform toreduce received noise, and wherein the waveform averaging modulecontinues averaging the corresponding digital waveforms from theanalog-to-digital converter.
 9. The apparatus of claim 8, wherein eachof the averaged digital waveforms is correlated by a correspondingcorrelator from the plurality of correlators to determine the time offlight.
 10. The apparatus of claim 6, wherein each of the correlators inthe plurality of correlators includes an first interpolating finiteimpulse response (FIR) filter for filtering the corresponding digitalwaveform to improve a time resolution of the time of flight estimate.11. The apparatus of claim 10, wherein each oft the correlators in theplurality of correlators includes an apply thresholds module forapplying a threshold value to the corresponding filtered digitalwaveform to ensure information data is being processed.
 12. Theapparatus of claim 11, wherein each of the correlators in the pluralityof correlators includes a peak detect module for detecting a peak in thefiltered digital waveform to compare against a peak in a transmittedlaser pulse generated by a laser.
 13. The apparatus of claim 12, whereinplurality of laser pulses are generated by the laser and transmitted bya rotating mirror, wherein the plurality of laser pulses are reflectedas the plurality of radio frequency pulses.
 14. The apparatus of claim13, wherein the rotating mirror rotates in a round robin manner for eachlaser pulse in the plurality of laser pulses.
 15. A method comprising:receiving, by a receiver, a plurality of radio frequency pulses, whereineach radio frequency pulse in the plurality of radio frequency pulsescorresponds to a pixel; digitizing, by an analog-to-digital converter,each radio frequency pulse into a corresponding digital waveform;determining, by a plurality of correlators, a time of flight for thecorresponding digital waveform; and determining, by a processor, animage of an object, based in part on the time of flight determined byeach of the plurality of correlators.
 16. The method of claim 15,wherein the plurality of correlators are one of four, eighteen, andeighty correlators working in parallel.
 17. The method of claim 16,wherein each of the correlators in the plurality of correlators includesan first interpolating finite impulse response (FIR) filter forfiltering the corresponding digital waveform to improve a timeresolution of the time of flight estimate.
 18. The method of claim 17,wherein each of the correlators in the plurality of correlators includesan apply thresholds module for applying a threshold value to thecorresponding filtered digital waveform to ensure information data isbeing processed.
 19. The method of claim 18, wherein each of thecorrelators in the plurality of correlators includes a peak detectmodule for detecting a peak in the filtered digital waveform to compareagainst a peak in a transmitted laser pulse generated by a laser. 20.The method of claim 19, wherein plurality of laser pulses are generatedby the laser and transmitted by a rotating mirror, wherein the pluralityof laser pulses are reflected as the plurality of radio frequencypulses.